This invention relates to novel zwitterion starch ether derivatives and to a method for their preparation. This invention also relates to modified zwitterion starch ether derivatives which contain, in addition to the zwitterion substituent groups, other cationic, cationogenic, or anionic substituent groups and to a method for their preparation. This invention also relates to the use of these novel zwitterion and modified zwitterion starch ether derivatives in various papermaking processes, especially to their use as pigment retention aids. This invention is also directed to a novel reagent useful for preparing the zwitterion starch ether derivatives.
As used herein, the term "zwitterion starch ether derivatives" includes amphoteric starch ether derivatives wherein the anionic and cationic or catiogenic substituent groups are both bonded to the same reaction site on the starch molecule through a zwitterion substituent group.
As used herein, the term "amphoteric starch ether derivatives" refers to a starch ether derivative wherein the anionic and cationic or cationogenic substituent groups are bonded to different reaction sites on the starch molecule.
As used herein, the term "cationogenic" refers to nonionic substituents capable of forming cations, e.g. diethylaminoethyl ether substituents.
As used herein, the term "paper" includes sheet-like masses and molded products made from fibrous cellulosic materials which may be derived from natural sources as well as from synthetics such as polyamides, polyesters, and polyacrylic resins, and from mineral fibers such as asbestos and glass. In addition, papers made from combinations of cellulosic and synthetic materials are applicable herein. Paperboard is also included within the broad term "paper".
It is well known to add cationic or anionic substituent groups to starch to form cationic or anionic starch derivatives. A discussion of the preparation of cationic or anionic starch ether derivatives may be found in "Starch: Chemistry and Technology", Vol. II, ed. by R. L. Whistler and E. F. Pascall (New York: Academic Press, 1967), pages 406-414 and 312-326, respectively.
It is also known to add both cationic and anionic substituent groups to starch to form amphoteric starch ether derivatives. Most of the prior art methods used to prepare amphoteric starch ether derivatives involve either an "in situ" formation of the amphoteric starch ether derivatives by simultaneous reaction of two different chemical modifying agents with the starch or a multi-step procedure wherein the chemical modifications of the starch are carried out in sequence. In the resulting starch ether derivatives, the cationic and anionic substituent groups are bonded to different reactive sites on the starch molecule. The "in situ" preparation of amphoteric starch ether derivatives is described in U.S. Pat. No. 3,459,632 and U.S. Pat. No. 4,119,487 and the multi-step procedure is described in U.S. Pat. No. 3,751,422.
It is also known to add cationic and anionic substituent groups to the same reactive site in the starch molecule, thereby forming zwitterion starch ether derivatives. The preparation of a zwitterion starch ether derivative, wherein the zwitterion substituent groups are aminocarboxylic acid groups, is described in U.S. Pat. No. 4,017,460. The derivatives are prepared by reacting the starch base directly with novel reagents obtained by reacting a secondary amine with a 2,3-dihalopropionic acid or an alkyl ester thereof. The resulting zwitterion group contains an anionic carboxyl group bound directly to a cationic amine group.
In contrast to the aminocarboxylic acid zwitterion starch ethers described in U.S. Pat. Nos. 4,017,460, the novel zwitterion starch ether derivatives of this invention contain, as the zwitterion substituent group, aminophosphonic acids (or their salts). Each substituent contains either one or two anionic methylenephosphonic acid groups bound to a cationic nitrogen.
In addition, the cationic or anionic characteristics of these zwitterion starch ether derivatives may be increased by the introduction of other cationic, cationogenic, or anionic substituent groups onto different reactive sites of the starch molecule.
It is well known to use starch and starch derivatives as aids in various papermaking processes such as wet end, sizing and coating applications. It is also known to use cationic, anionic, and amphoteric starch ether derivatives as pigment retention aids. In the case of paper containing added pigments, these pigment retention aids are added to the pulp or stock during the papermaking process for the specific purpose of retaining a greater proportion of such pigments in the paper (rather than have them drain off in the water that is removed during the formation of the sheet). A particularly desirable pigment retention aid would be one which is versatile and which may be used in both neutral and acidic systems (contains alum). Hence, the search continues for novel starch ether derivatives which will improve pigment retention in paper, while being at the same time relatively facile and inexpensive to prepare.
Accordingly, it is an object of the present invention to provide novel zwitterion starch ether derivatives wherein one or two methylenephosphonic acid groups (or salt groups) are bonded to a cationic nitrogen atom and to provide a novel reagent and a method for preparing them.
It is a further object to provide modified zwitterion starch ether derivatives which contain, in addition to the zwitterion substituent groups, additional cationic, cationogenic or anionic substituent groups on different reactive sites of starch and to provide a method for preparing them.
It is further object to provide novel zwitterion and modified zwitterion starch ether derivatives which will be useful in various papermaking processes, especially as pigment retention aids.
It is a further object to provide a paper with improved pigment retention.